1) Megabase-sized and plasmid (circular) DNA species were separated by electrophoresis in a constant field, using uncrosslinked polyacrylamide of molecular weight 5,000,000 as retarding polymer solution. The method enhances the simplicity of separations of chromosomal sized DNA compared to present pulsed field methods and surpasses their analytical, and particularly their preparative potential. 2) Agarose melted and maintained above its gelling temperature was shown to be a highly effective liquid separation medium for circular DNA species (3 to 16 kb) and polystyrene sulfate size standards (0.2 to 2 micron in diameter). The applicability of capillary electrophoresis apparatus to rapid and quantitative size separations of DNA in agarose above its gelling temperature was demonstrated. 3) Hydroxypropylmethylcellulose (HPMC) was evaluated as a liquid sieving medium. 4) Pattern analysis in transverse polyacrylamide pore gradient gel electrophoresis was automated. The method provides automated detection of DNA with abnormal conformational or surface net change characteristics in a mixture. It surpasses assay for detection of bent and protein-bound DNA. 5) The relative economy in separation time, using a scanning detector rather than a fixed detector position, was demonstrated. 6) Mechanisms underlying agarose gel electrophoresis and Field Inversion Gel Electrophoresis (FIGE) of DNA were studied by measurements made with the epifluorescence video microscope. These account for the observed non-monotonic relation between size and mobilities of large DNA in FIGE.